Electrode comb and method and device for manufacturing

ABSTRACT

A single piece electrode comb or device includes two circuit boards having conductor paths and two separate rows of needle-like recording electrodes which are electrically connected to separate paths of the respective circuit board encapsulated in a single plastic resin body with the electrode rows extending to a recording edge formed in a rib along one edge of the body. To form the electrode comb, a device having two substantially similar rectangular cross-sectional shaped halves is assembled in one position to form a winding core on which a wire is wound with a plurality of turns, clamped and joined to the respective circuit boards which are mounted on faces of the two halves, subsequently the wires are separated along a parting plane and the two halves are disassembled with one being rotated 180° relative to its previous position so that the faces with the recesses are adjacent each other to form a casting mold into which a plastic resin is injected to encapsulate the wires which after hardening of the plastic are trimmed back at least along the recording edge.

This is a division of application Ser. No. 488,380, filed Apr. 25, 1983,which issued as U.S. Pat. No. 4,540,151 on Sept. 10, 1985.

BACKGROUND OF THE INVENTION

The present invention is directed to an electrode comb or device and adevice and method for manufacturing an electrode comb which has at leasttwo rows of wire pieces acting as needle-like recording electrodes whichare arranged in a rib of a molded body with the wires of one row beingoffset by half the distance between the wires of the second row. Themethod and the device include providing a mold member composed of twohalves which are assembled together in one position to form a windingcore which has recesses on opposite outer surfaces and on which a wireis wound with the turns being joined to circuit boards disposed in therecesses clamped and severed. Then the two halves are disassembled andreassembled with the recesses facing each other to form a mold cavityinto which a resin compound is injected to form the electrode comb.Subsequent to hardening of the resin compound, the exposed ends of thewires are trimmed to be flush with the surface of a recording edge ofthe molded body.

Electrode combs which have at least one row of needle-like recordingelectrodes are required for producing exact copies of a master on a copypaper. The combs are utilized to charge point-by-point the copy paper inaccordance with the electrode arrangement so that a toner will adhere tothe corresponding points when it is applied. In order to obtain a highrecording quality of eight points per millimeter, the electrodes areusually disposed in two rows having respective spacing of 250 um and theelectrodes in one row are offset by 125 um from the electrodes of theother row. Thus, the electrode comb generally contains up to 2000recording electrodes, which are disposed parallel to one another and arefixed by means of a thermosetting plastic resin. For the purpose ofmanufacturing such needle electrodes, a wire is usually wound on awinding core or mold with each turn of the winding having a specificlead or pitch. After the individual windings are fixed with theassistance of the thermosetting resin, the individual windings are againsevered.

A device for manufacturing an electrode comb composed of numerousneedle-shaped electrodes is disclosed by German LP No. 22 61 529. Amulti-part mold having an upper and lower mold part is utilized. Thelower mold part has a planar top surface and an essentially convexlycurved underside. In the upper area or top surface, lateral faces of thelower mold part have planar surface parts against which printed circuitboards are seated. After a wire has been wound around the lower moldpart, each of the turns is connected such as by soldering to conductorpaths or circuits of each circuit board. The upper surface of the lowermold part has two rectangular recesses which extend parallel to oneanother and to the longitudinal axis of the part and these recessesreceive an injection or casting resin compound. An upper mold part has asurface corresponding to the upper surface or the lower mold part withcorresponding recesses. Thus, after a wire has been wound on the lowermold part with the windings having a predetermined, mutual spacing andthe wires being secured to the appropriate conductor paths in thecircuit boards, the upper mold part is then placed on the upper surfaceof the lower mold part. Subsequently, the resin compound is injectedinto the cavities of the two mold parts to form two resin strips with arespective row of recording electrodes therein. After hardening of theresin, the part of the wire winding extending between the two recessesis cut so that two units with each having a resin strip containing a rowof needle-shaped electrodes are produced. The two faces of these twoparts are joined together to form the electrode comb. The joining of thetwo strips must be undertaken with the needle electrodes of the two rowsbeing mutually offset so that the needles of the one row arerespectively opposite the space between the two needles of the other rowand such that the ends of the needles proceed in two straightlongitudinal rows from one end to the other end of the part. Thispresupposes not only a very precise manufacturing of the stripscontaining the rows of electrodes but a rather precise joining of thetwo strips as well. Another disadvantage of the comb provided in thismanner is that the strips containing the rows of electrodes areconnected to each of the printed circuit boards only by the flexiblewires of the winding so that there is always the hazard of damaging theindividual wires.

SUMMARY OF THE INVENTION

The present invention is directed to a one-piece electrode comb whichforms a compact unit together with its circuit boards and to a methodand device utilized in manufacturing this electrode comb.

To obtain these objects, the present invention is directed to anelectrode comb having two rows of needle-shaped recording electrodesexctendin to a recording edge, said comb comprising a one-piece moldedbody of a resin compound having a rib with said recording edge along oneedge of the body, said body containing two circuit boards with conductorpaths and two rows of needle-shaped recording electrodes with theelectrodes of one row being connected to the circuit paths of onecircuit board and the electrodes of the other row being connected to thecircuit paths of the other circuit board, the electrodes of each rowbeing evenly spaced apart and said two rows of needle-shaped electrodesextending to an outer surface of said recording edge of said rib withthe electrodes of one row being offset from the electrodes of the otherrow by an amount equal to one-half the spacing between the electrodes ofeach row.

To produce such an electrode comb, the present invention is alsodirected to a device comprising a mold member being composed of twosymmetrically constructed halves with a rectangular cross-section, eachhalf having a first face with a flat planar surface, a second faceopposite the first face having a first recess for receiving a circuitboard and a second recess separated from the first recess by a supportsurface, third and fourth faces extending between the first and secondfaces, each of said third and fourth faces having recesses adjacent thefirst face, one of the third and fourth faces having means for clampingwires to said surface; means for holding the halves with said firstsurface engaging each other to form a parting plane of a winding corewith the second faces being faced in the opposite direction to receivecircuit boards in each of the first recesses, and means for holding thetwo halves together with the second faces adjacent each other to form afirst mold cavity from the first recesses and a second mold cavity fromthe second recesses with the two rows of wires extending through saidcavities.

The method of the present invention utilizes the above mentioned deviceand after having the two halves held together with the first facesforming the parting plane of the winding core, includes inserting acircuit board in each of the first recesses, winding a wire around thewinding core while maintaining the desired spacing and pitch of eachturn, then securing each of the wires to the respective circuit paths ofthe circuit boards, clamping the wires with the clamping means to eachhalf, then severing the wire of each turn at two points adjacent theparting plane, disassembling the two halves and reassembling the halvesof one of the halves being rotated 180° so that the second faces areadjacent each other to form the mold cavities with the wires extendingtherethrough; injecting a molding compound such as a resin compound intoeach of the mold cavities subsequently after the resin compound hardenstrimming the exposed portions of the wires to lie flush with thesurfaces of the molded material.

The symmetrical design of each of the halves of the mold membersignificantly facilitates the manufacture of the electrode comb. Afterwinding the wire onto the winding core and electrically contacting eachof the turns to its respective circuit path in the circuit board, theelectrode comb can be manufactured in a single casting operation withall of the wires forming the needle electrodes being in the desired rowwith the corresponding spacing. The flat recesses in the winding halvesof the winding core for the printed circuit boards are preferablydesigned so that the circuit boards lie symmetrically at an acute anglerelative to the planar surface of the second face and also to the planarsurface of the first face. Thus, the manufacture of a compactlyencapsulated single piece electrode comb with the printed circuit boardsincluded therein is possible. This has the considerable advantage thatshorts and wire breaks are reliably excluded. The slightly slantingdisposition of the circuit boards moreover also guarantees a reliablesupport of each of the wires against the support stay or surface of thesecond face. Thus, the needle-like recording electrodes are disposedprecisely parallel and the two winding halves are pinned obliquelyrelative to one another during the casting operation in order tocompensate for the angle of thread pitch. An additional support surfaceis also advantageously provided so that the two wire position planes lieparallel to each other. The additional support surface is manufacturedwithout a thread pitch for the reason of fabrication technology. Thewires are covered with a template immediately after they are wound andare secured with a spray lacquer only in the support area so that theymay retain the precision of the winding pitch.

Fiberglass reinforcing strips can be inserted into the second recessesin order to stiffen the electrode comb in the comb area. The positioningof the reinforcing strips preferably occurs with conical pins so thatthe mold parts can be easily separated after the molding operation.

In a preferred embodiment, the bottom surface of the recess receivingthe circuit boards is equipped with channels which have a truncatedtriangular cross-section. They serve for suctioning of the connectingplates provided with a suction bore when the leads are soldered onto thecircuit paths. The truncated triangular cross-section of the channelsenables easy disassembly of the cast parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view taken on the lines I--I of FIG. 3 ofthe device of the present invention while assembled as a winding core;

FIG. 2 is a cross-sectional view similar to that of FIG. 1 with thedevice of the present invention assembled as a casting mold; FIG. 3 is aside view of the device of the present invention assembled as a windingcore as illustrated in FIG. 1;

FIG. 4 is a bottom view of the device of the present invention assembledas a winding core as illustrated in FIG. 1;

FIG. 5 is a top view of the device of the present invention assembled asa casting mold as illustrated in FIG. 2;

FIG. 6 is a side view of an electrode comb manufactured in accordancewith the present invention with portions broken away for purposes ofillustration;

FIG. 7 is an end view of the electrode comb of FIG. 6;

FIG. 8 is a top view of the electrode comb of FIG. 6; and

FIG. 9 is an enlarged cross-sectional view taken on the lines XI--XI ofFIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles of the present invention are particularly useful forproducing an electrode comb or device (see FIGS. 6-9) 46 which has abody portion 50 that has a resin strip or rib 40 extending along oneedge. The resin strip 40 on an outer surface has a recording edge 39. Ateach end of the body 50, reinforcing ribs 51 and 52 are provided. Thebody between the reinforcing ribs 51 and 52 and the rib 40 tends totaper in thickness from a maximum size at an edge 53 opposite the rib 40to a minimum thickness adjacent the rib 40.

The device or comb 46 includes a pair of circuit boards 10 and 12 whichhave a plurality of conductor paths which are connected by ribbonconductors 36 that exten out of the ends of the body 50 for connectionto a control circuit. In addition, the device 46 has a first row 55(FIG. 9) of needle-shaped recording electrodes with each of theelectrodes having an even spacing and being connected to separateconductor paths of the circuit board 10. In a similar manner, a secondrow 56 of needle-shaped recording electrodes are connected to theconductor paths of the circuit board 12. Both rows 55 and 56 while inthe rib 40 extend parallel to each other with the electrodes of the row56 being positioned to be offset by half the spacing therebetween fromthe electrodes of the row 55 so that the electrode in the row 56 isopposite a space between two adjacent electrodes in the row 55. Asillustrated, the electrodes in both rows 55 and 56 extend to therecording edge 39.

In order to manufacture or produce the device 46, the present inventionis directed to a device or mold member generally indicated at 1 in FIG.1 which member is composed of two halves 2 and 3 which are symmetrical.When the halves are arranged as illustrated in FIG. 1, the device ormold forms a winding core and when the halves 2 and 3 are assembled asillustrated in FIG. 2, the device 1 then is a casting or injection mold.

As illustrated, each of the halves 2 and 3 have a substantiallyrectangular cross-section with a first face 11 which has a flat planarsurface. Opposite the first face 11, each of the halves has a secondface 60 which is interconnected to the first face 11 by a third face 61and a fourth face 62. As mentioned hereinabove, each of the halves 2 and3 is absolutely identical with the sole difference being that the half 3has two set pins 4 which extend from the second face 60 and are receivedin corresponding bores that are provided in the second face 60 of thehalf 2 to enable assembling the two halves as a casting mold asillustrated in FIGS. 2 and 5. The adjustment or positioning of the twohalves 2 and 3 while assembled as illustrated in FIGS. 1, 3 and 4 toform a winding core is obtined by means of set pins 5 which are insertedin corresponding bores 6 of the two halves. The device 1 includes meansfor holding the two halves together in both the winding position asillustrated in FIG. 1 and in the molding position as illustrated in FIG.2 which means utilizes four sets of nuts and bolts 7 (FIG. 3).

The second face 60 of the half 2 has a rectangular recess 8 whichreceives a circuit board 10. In a similar manner, the second face 60 ofthe half 3 has a recess 9 for receiving the circuit board 12. The recess8 has a bottom or inclined surface 64 while the recess 9 has a bottominclined surface 65 and each of the bottom or inclined surfaces 64 and65 extend in a plane that forms an acute angle with both the remainingsurfaces of the face 60 as well as the plane of the surface forming thefirst face 11. As illustrated, these two planes of the bottom surfaces64 and 65 are symmetrical relative to the plane of the first faces 11.The second face 60 of the first half immediately below the recess 8 hasa recess 13 which is spaced by a support surface 15 therefrom. In asimilar manner, the second half 3 on the second face 60 has a recess 14which is spaced from the recess 9 by a support surface 16. The supportsurfaces 15 and 16, as will be explained hereinafter, form support staysfor holding the individual turns of a wound wire 17 which is indicatedin dot-dash lines in FIGS. 1 and 2.

As illustrated in FIGS. 1 and 2, the third face 61 of the half 2 has arecess 23 adjacent the first face 11. In a similar manner, the fourthface 62 has a recess 23'. The other half or second half 3 on its thirdface 61 has a recess 24 adjacent the first face 11 and the fourth face62 has a recess 24' adjacent the first face 11. In addition, the cornerbetween the third face 61 and the second face 60 of the half 2 isprovided with a bevel 18 while the corner between the second face 60 andthe fourth face 62 is provided with a bevel 18'. In a similar manner,the corner between the first face 60 and the third face 61 of the secondhalf 3 has a bevel 19 with a bevel 19' being positioned at the cornerbetween the fourth face 62 and the second face 60. Each of these bevels18, 18', 19 and 19' can be provided with means 20 for maintaining amutual spacing and pitch for a wire 17 which is wound on the core. Thismeans 20 can be a series of grooves as illustrated in FIG. 3.

After the circuit boards 10 and 12 have been inserted in the recesses 8and 9 of the halves 2 and 3 which are arranged as a winding core, a wire17 is wound onto the two halves with the turns of each winding having aslight lead of approximately 250 um in a circumferential direction. Inorder to hold the turns of the wire precisely as determined, the means20 for maintaining a predetermined mutual spacing between turns andpitch for the turns is utilized. After the individual turns have beenwound and contacted to the corresponding circuit paths of each of thecircuit boards 10 and 12 such as by soldering, the winding wire 17 isclamped by means of clamp strips 21 and 22 which are received in therecesses 23 and 24 of the halves 2 and 3 adjacent the third face. Theclamp strip 21 coacts with a clamp strip 25 that is urged into tightengagement therewith by threaded member such as screws 27. In a similarway, the clamp strip 22 coacts with a clamp strip 26 which is urgedthereagainst by threaded fasteners or screws 28. In addition, therecesses 23' and 24' which are associated with the fourth surfacereceive clamp strips 21' and 22' respectively. Each of these clampstrips 21' and 22' are provided with a sawtooth configuration 29 (FIG.4) with the saw teeth extending opposite to the direction of tension onthe wire. Each of the clamp strips such as 21 and 21', 22 and 22' aswell as the strips 25 and 26 are composed of hardened steel. In order tomaintain a prestress on the wound turns of the wire 17, rubber strips 30are provided on the surfaces of the faces 61 and 62 of the first half 2while the second half 3 has rubber strips 31 on its face 61 and 62.

After winding the wire 17 onto the core which is formed with the halves2 and 3 assembled as illustrated in FIGS. 1, 3 and 4, the wire isclamped as mentioned and then the turns are cut or severed on theparting plane 11 or parallel thereto. This cutting can be done byutilizing a double guillotine shear 32 which coacts with the hardenedstrips such as 21' and 22' to cut the wires. After severing the turns,the halves 2 and 3 are disassembled and one of the halves such as thehalf 2 with its clamped wires 17' is rotated through 180° so that thesecond faces 60 of the two halves are facing each other as illustratedin FIG. 2 with the two rows of wires 17' and 17". As mentionedhereinbefore, the set pins 4 of the half 3 are received in the bores ofthe half 2 to determine the alignment.

With the halves 2 and 3 assembled in the second position such asillustrated in FIG. 2, the recesses 8 and 9 form a first cavity 34 whichhas a wedge-shaped cross-section due to the fact that the bottomsurfaces 64 and 65 extend at an angle to the surface of the second faces60. Thus, the circuit boards 10 and 12 will assume a slightly inclinedposition relative to one another and be symmetrical to a comb plane 33whereas the surfaces of the support surfaces 15 and 16 are disposedparallel to one another. In addition, the recesses 13 and 14 will form asecond cavity 70 which, after it is filled with the plastic resin, willeventually form the rib or resin strip 40 which is best shown in FIG. 9.The resin is inserted into the cavity from the top as indicated by thearrow A and in order to prevent lateral escape of the resin, sealingstrips 35 (FIGS. 3-5) are provided and act to terminate the cavity toform the ends of the body 50. The sealing strips 35, however, do allowthe tape-shaped leads 36 of each circuit or printed circuit board 10 and14 to be passed through the end of the mold. To facilitate this,web-shaped emission openings or grooves 37 (FIGS. 3-5) are provided ineach of the halves 2 and 3. Each of the cavities or recesses, whichreceive the circuit boards as best illustrated in FIGS. 4 and 5 adjacentthe sealing strips 35, are enlarged as indicated at 71 so that thecavity 34 has enlarged cavities or portions 38 to produce the end beadsor ribs 51 and 52 as illustrated in FIG. 6. These enlarged beads 51 and52 act to stabilize the body 50.

After the cavities 34 and 70 have been filled, the actual recording edge39 will occur at a lower end of the cavity 70 as illustrated in FIG. 2.The projecting portion of the wires 17' and 17" are trimmed and removedat the recording edge 39 to be flush with the surface thereof. Thus, thewires that remain are the pieces which are embedded in the rib 40 andform the actual needle-shaped recording electrodes. So that the changesin the presentation patterns are not produced in the followup work ofthe recording edge 39, the wires must be conducted to extend parallel toone another at least in the rib portion 40. To this end, the halves 2and 3 when pinned together are pinned at a slight relative slant to oneanother in order to compensate for the angle of the thread pitch duringwinding of the wire 17 on the winding core.

In order to reinforce the rib 40, it is desirable to include fiberglassreinforcing strips 41 and 42 as illustrated in FIG. 9. In order to dothis, the strips 41 and 42 are inserted in the recesses 13 and 14(FIG. 1) prior to filling the mold with the resin. To hold the strips inthe particular recesses 14 and 13, conical pins 43 are provided andenable easy removal of the molded part with the reinforcing strips afterthe molding operation. The conical pin will leave conical pin holes 43'(FIG. 9) which serve as fixing points in the cast comb for the first plyof the wound wire.

Each of the bottom surfaces 64 and 65 of FIG. 1 can be provided withparallel channels such as 44 (FIG. 3) for the bottom surface 65. Each ofthese channels taper down to a bottom which is flat so that they have asubstantially truncated triangular cross-section. The grooves 44 servethe purpose of suctioning the circuit or printed circuit boards 10 or 12with a suction bore when the conductor paths are soldered to theindividual wire turns. The particular cross-sectional shape of each ofthe channels 44 enable easy removal of the cast part from the mold afterthe molding operation.

The adjustment of the circuit or printed circuit boards preferablyoccurs after the winding of the wire on the core. Pins 45 (FIG. 3) servethe purpose of pre-centering and therefore exhibit a fitting sleevewhich can be removed from above for adjustment after the winding step.

As mentioned hereinabove, to provide a connection for each of theneedle-shaped electrodes of a single row, a single circuit board isprovided and has a plurality of conductor paths. The electrodes areconnected to the individual conductor paths in a grid dimension ofapproximately 250 um. At the same time, a test electrical strength of500 volts must be guaranteed. In order to achieve this, each of theconductor paths of the circuit board are completely covered with atemperature-proof insulation so that the solderable insulation of theneighboring wire is not destroyed from below due to the thermalconductivity of the conductor paths.

For increasing the electrical and thermal insulation, the tracks orpaths of the circuit boards are preferably completely provided with thetemperature-proof insulation and are only exposed at those points wherethey are to be connected to an electrode. If need be, these exposedareas can be metallically elevated up to the upper edge of theinsulating layer and can be provided with a solder surface for areliable connection.

Although various minor modifications may be suggested by those versed inthe art, it should be understood that we wish to embody within the scopeof the patent granted hereon, all such modifications as reasonably andproperly come within the scope of our contribution to the art.

We claim:
 1. A method of forming an electrode comb having two rows ofneedle-shaped recording electrodes connected to two circuit boards andembedded in a one-piece molded body of resin having a rib with arecording edge along one edge of the body with the recording electrodesextending to a surface of said recording edge, said method comprisingthe steps of providing a mold comprising two symmetrically constructedhalves with a rectangular cross-section, each half having a first facewith a flat planar surface, a second face opposite the first face havinga first recess for receiving a circuit board with conductor paths, asecond recess separated from the first recess by a support surface,third and fourth faces extending between the first and second faces,each of the said third and fourth faces having a recess adjacent thefirst face, and said third face having means for clamping the wires tosaid surface; assembling the halves with the first surfaces engagingeach other to form a parting plane of a winding core with the secondface facing in an opposite direction; assembling a circuit board in eachof said first recesses; winding a wire around the core with equalspacing and pitch between turns; clamping the wound wire to each of thehalves; electrically connecting each of the turns to its respectivecircuit board; severing the wire turns in two places adjacent theparting plane; disassembling the two halves and rotating at least one ofthe two halves 180° to the other half to reassemble the halves with thesecond faces adjacent each other to form a casting mold with a firstmold cavity formed by the first recesses containing the circuit boardsand a second mold cavity being formed by the second recesses with therows of wires extending therethrough and offset from each other;injecting a resin into each of said mold cavities; and subsequent to thehardening of said resin, trimming the exposed wires extending from eachcavity to form the electrode comb having a rib with the recording edgeformed by the resin in the second cavity.
 2. A method according to claim1, wherein the step of providing the halves provides each of the halvesadjacent the second recess with guide means for the wire during thewinding step, and wherein said step of winding includes guiding eachturn of the wire into the guide means to maintain the desired spacingand pitch for each of the turns.
 3. A method according to claim 1, whichincludes the step of inserting reinforcing strips in each of the secondrecesses prior to the step of winding the wire onto the winding core.